Adaptive rollover detection apparatus and method

ABSTRACT

A vehicle rollover detection apparatus and method are provided for detecting an overturn condition of the vehicle. The rollover detection apparatus includes an angular rate sensor sensing angular rate of the vehicle, and a vertical accelerometer for sensing vertical acceleration of the vehicle. A controller processes the sensed angular rate signal and integrates it to produce an attitude angle. The vertical acceleration signal is processed to determine an inclination angle of the vehicle. The rollover detection apparatus adjusts the attitude angle as a function of the inclination angle and compares the adjusted attitude angle and the processed angular rate signal to a threshold level to provide a vehicle overturn condition output signal. Additionally, the rollover detection apparatus detects a near-rollover event and adjusts the variable threshold in response thereto to prevent deployment of a vehicle overturn condition, thus providing immunity to such events.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 10/005,990,entitled “ADAPTIVE ROLLOVER DETECTION APPARATUS AND METHOD,” filed onNov. 8, 2001 now U.S. Pat. No. 6,522,963, and is a continuation-in-partof application Ser. No. 09/725,645 entitled “VEHICLE ROLLOVER DETECTIONAPPARATUS AND METHOD.” filed on Nov. 29, 2000 and now U.S. Pat. No.6,542,792.

TECHNICAL FIELD

The present invention generally relates to rollover sensors and, moreparticularly, to cost affordable vehicle rollover detection with reducedsensor hardware and enhanced rollover discrimination for sensing arollover condition of a vehicle.

BACKGROUND OF THE INVENTION

Automotive vehicles are increasingly equipped with safety-relateddevices that deploy in the event that the vehicle experiences a rolloverso as to provide added protection to the occupants of the vehicle. Forexample, upon detecting a vehicle rollover condition, a pop-up roll barcan be deployed such that, when activated, the roll bar further extendsvertically outward to increase the height of support provided by theroll bar during a rollover event. Other controllable features mayinclude deployment of one or more air bags, such as frontal air bags,side mounted air bags, and roof rail air bags, or actuating apretensioner to pretension a restraining device, such as a seat belt orsafety harness, to prevent occupants of the vehicle from ejecting fromthe vehicle or colliding with the roof of the vehicle during a rolloverevent.

In the past, mechanical-based rollover sensors have been employed inautomotive vehicles to measure the angular position of the vehicle fromwhich a rollover condition can be determined. The mechanical sensorshave included the use of a pendulum normally suspended verticallydownward due to the Earth's gravitational force. Many mechanicalautomotive sensing devices are employed simply to monitor the angularposition of the vehicle relative to a horizontal level ground position.As a consequence, such mechanical automotive sensors have generally beensusceptible to error when the vehicle travels around a corner or becomesairborne, in which case the Earth's gravitational force, which thesensor relies upon, may be overcome by other forces.

More sophisticated rollover sensing approaches require the use of asmany as six sensors including three accelerometers and three angularrate sensors, also referred to as gyros, and a microprocessor forprocessing the sensed signals. The three accelerometers generallyprovide lateral, longitudinal, and vertical acceleration measurements ofthe vehicle, while the three gyros measure angular pitch rate, rollrate, and yaw rate. However, such sophisticated rollover sensingapproaches generally require a large number of sensors which add to thecost and complexity of the overall system. In addition, many knownsophisticated sensing systems are generally susceptible to cumulativedrift errors, and therefore occasionally must be reset.

In an attempt to minimize the number of sensors required, someconventional rollover sensing approaches have employed, at a minimum,both an angular roll rate sensor and lateral accelerometer. For thosesensors designed to detect both rollover and pitchover events, anangular pitch rate sensor and a longitudinal accelerometer are typicallyadded. While the angular rate sensor can be integrated to calculate aroll angle, in practice, angular rate sensors typically generate anon-zero, time-varying output, even in the absence of a roll rate. Thisbias may cause a significant error in the integration generated rollangle, and such bias must be compensated in order to provide an accuratesensed measurement. Accordingly, many conventional rollover sensingapproaches typically require auxiliary sensors, in addition to theangular rate sensor, to compensate for zero-input biases inherent inmany angular rate sensors.

Another rollover sensing approach is disclosed in related applicationSer. No. 09/725,645 entitled “VEHICLE ROLLOVER DETECTION APPARATUS ANDMETHOD,” filed on Nov. 29, 2000, which is commonly assigned to theassignee of the present application. The aforementioned approach employsan angular rate sensor generating a sensed roll rate signal which isintegrated to produce a roll angle. The roll angle and sensed roll ratesignals are processed by a microprocessor-based controller to generate arollover deployment signal. This approach also employs a bias removaldevice which removes bias. However, this approach may require a partialreset when the integration window is contracted, which places a largecomputational burden on the microprocessor. In addition, microprocessorconstraints on random-access memory (RAM) limit the width of theintegration window, placing an upper limit on the maximum duration of arollover event that can be properly sensed. This generally can result insmall errors in the roll angle which could have an effect onconcatenated events such as two-stage cross slope rollovers.Additionally, it remains difficult to ascertain a forthcoming rolloverevent for certain very near-rollover events.

Accordingly, it is therefore desirable to provide for an accurate andcost affordable rollover detection apparatus and method that minimizessignal bias. It is further desirable to provide for a rollover detectionapparatus and method that provides improved immunity to non-rolloverconditions during near-rollover events so as to prevent false rolloverdeployments during these driving events.

SUMMARY OF THE INVENTION

In accordance with the teachings of the present invention, a vehiclerollover sensing apparatus and method are provided for detecting ananticipated overturn condition of a vehicle, and thus allowing for thetimely deployment of safety-related devices. The rollover sensingapparatus includes an angular rate sensor for sensing attitude rate ofchange of a vehicle and producing an angular rate signal indicativethereof, and a vertical accelerometer for sensing vertical accelerationof the vehicle and producing a vertical acceleration signal indicativethereof. The rollover sensing apparatus also has a controller includingan integrator for integrating the attitude rate signal and producing anattitude angle. The controller determines an inclination angle of thevehicle based on the vertical acceleration signal and adjusts the rollangle as a function of the determined inclination angle. The controllerfurther includes deployment logic for comparing the adjusted attitudeangle and angular rate signal to a threshold limit, and providing avehicle overturn condition signal based on the comparison.

According to another aspect of the present invention, a rolloverdetection apparatus and method is provided for detecting an anticipatedoverturn condition for a vehicle and providing immunity to near-rolloverevents. The apparatus comprises an angular rate sensor for sensingattitude rate of change of a vehicle and producing an attitude ratesignal indicative thereof, an integrator for integrating the sensedattitude rate of change signal and producing an attitude angle, anddeployment logic. The deployment logic compares the attitude angle andsensed attitude rate signal with a variable threshold defining a regionof deployment and a region of no deployment. The deployment logicfurther detects the presence of a driving event, such as a near-rolloverevent, which causes at least one of a large attitude rate and a largeattitude angle, and adjusts the variable threshold based on detectingthe driving event so as to prevent deployment of a vehicle overturncondition. The output provides a vehicle overturn condition signal basedon the comparison.

Accordingly, the rollover sensing apparatus and method of the presentinvention advantageously provides enhanced rollover detection with aminimal number of sensors to detect an overturn (e.g., rollover)condition of a vehicle. It should be appreciated that the apparatus andmethod employs an angular rate sensor and vertical accelerometer,without requiring other auxiliary sensors, to achieve cost efficient andaccurate rollover detection. It should further be appreciated that theapparatus and method provide enhanced immunity to false rollover events,such as those events that approach a near-rollover condition.

These and other features, advantages and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims and appendeddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a block diagram of a rollover sensing module for detectingvehicle rollover according to the present invention;

FIG. 2 is a block diagram further illustrating the rollover sensingaccording to the present invention;

FIG. 3 is a block/flow diagram illustrating a rollover sensing algorithmfor detecting vehicle rollover with the rollover sensing moduleaccording to the present invention;

FIG. 4 is a graph illustrating regions of operation of the adaptive biasremoval with output minimum (ABROM) logic;

FIGS. 5A and 5B are a flow diagram illustrating the central routine forthe integrator with intelligent drift removal;

FIG. 6 is a graph illustrating a gray-zone duration indicator employedby the deployment logic;

FIGS. 7A and 7B are a flow diagram illustrating the central routine forthe deployment logic with gray-zone duration indicator and near-rolloverimmunity;

FIG. 8 is a flow diagram illustrating the central routine for theadaptive bias removal with output minimum logic;

FIG. 9 is a graph illustrating bias removal from a sensed signalachieved with the adaptive bias removal with output minimum logic; and

FIG. 10 is a graph further illustrating bias removal from a sensedsignal achieved with the adaptive bias removal with minimum outputlogic.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a rollover sensing module 10 is illustrated for usein sensing roll angular rate of a vehicle and detecting a rollovercondition of an automotive vehicle (not shown). The rollover sensingmodule 10 of the present invention is preferably mounted on anautomotive vehicle and is used to detect, in advance, a future rolloverevent (condition) of the vehicle. A vehicle rollover condition, asdescribed herein in connection with the present invention, may includeside-to-side rotation of the vehicle about the longitudinal axis of thevehicle, commonly referred to as a “vehicle rollover,” or back-to-frontrotation about the lateral axis of the vehicle, commonly referred to asa “vehicle pitchover,” or a combination of rollover and pitchover. Forpurposes of describing the rollover sensing of the present invention,the term “rollover” is generally used to refer to either a rollovercondition or a pitchover condition.

The rollover sensing module 10 is designed to be located in anautomotive vehicle to sense vehicle dynamics and to detect a rollovercondition of the vehicle. Upon detecting a vehicle rollover condition,the rollover sensing module 10 provides a rollover deployment commandsignal indicative of the detected rollover condition. The rolloverdeployment command signal may be supplied to one or more selectedvehicle devices, such as safety-related devices, to deploy the device(s)in anticipation of an upcoming rollover event. The detected rollovercondition output signal may be employed to deploy a pop-up roll bar toprovide vertical clearance to the occupants of the vehicle as thevehicle rolls over. Similarly, the detected rollover deployment outputsignal may actuate an occupant restraining device, such as a seat beltor harness safety pretensioner, to eliminate slack in the restrainingdevice just prior to the vehicle rollover event occurring. Other controlfunctions include deployment of front, side or roof rail (side curtain)deployment air bags to protect the vehicle occupants during a vehiclerollover. These and other devices may be controlled in response to therollover deployment output signal.

The rollover sensing module 10 includes two sensors for detecting arollover condition and generating a rollover deployment decision, withboth sensors preferably assembled together on module 10, and each sensororiented to perform the intended sensing operation. The sensors includea roll angular rate sensor 12 and a low-g vertical accelerometer 14 foruse in detecting vehicle rollover. The roll angular rate sensor 12measures the time rate of angular roll about the longitudinal axis ofthe vehicle. The low-g vertical accelerometer 14 measures the verticalacceleration of the vehicle, particularly for low-g accelerations. Low-gaccelerations may include minus five (−5) to plus five (+5) gs,according to one example. In addition, a high-g lateral accelerometer 16is also shown assembled on module 10 for detecting lateral(side-to-side) acceleration of the vehicle particularly for high-gaccelerations. High-g accelerations may include minus thirty-five (−35)gs to plus thirty-five (+35) gs, according to one example. The lateralacceleration signal is used as an input to an arming algorithm, whichmay or may not be employed for determining the rollover deploymentcommand signal.

While the rollover detection of the present invention is describedherein for determining vehicle rollover about the longitudinal axis ofthe vehicle, it should be appreciated that the present invention may beconfigured to provide pitchover detection about the lateral axis of thevehicle. In order to provide pitchover detection, a pitch angular ratesensor would be employed in place of the roll angular rate sensor 12,and the high-g lateral accelerometer would be replaced by a high-glongitudinal accelerometer to provide the input to the arming function.It should be readily apparent to those skilled in the art that pitchoverdetection may require different threshold values, in contrast torollover detection. It should further be appreciated that both rolloverand pitchover detection may be achieved by employing both roll and pitchangular rate sensors.

The rollover sensing module 10 further includes a microprocessor controlunit (MCU) 20 for processing sensed vehicle parameters according to arollover detection algorithm to detect vehicle rollover conditions. MCU20 is preferably a microprocessor-based controller and, according to oneexample, may include Model No. 68HC08, made available by Motorola.Associated with MCU 20 is an electrically erasable programmableread-only memory (EEPROM) 22 that stores various programmed calibrationsfor performing the rollover detection algorithm, as is explained herein.The EEPROM 22 can be integrated with the MCU 20 or provided externalthereto.

Rollover sensing module 10 also includes a power and communicationinterface 26 for receiving an ignition (IGN) signal on line 28 andcommunicating via serial data (SDATA) on serial data bus 32. Rolloversensing module 10 is further grounded via ground (GND) line 30. Powerand communication interface 26 converts an approximately 12-volt DC IGNsignal input to 5-volts DC for use as a power supply to the poweredcomponents on module 10. Serial data communicated on serial data bus 32may include individual sensor outputs and processor outputs, as well asprogrammed inputs.

MCU 20 receives, as inputs, signals from each of angular rate sensor 12,vertical accelerometer 14, and lateral accelerometer 16. In addition,the MCU 20 may receive other various inputs which, although notrequired, may be employed in connection with the rollover detection anddeployment of the present invention. These other inputs may include apassenger presence signal, which may be generated as a sensed outputfrom an occupant presence sensor for purposes of sensing the presence ofa passenger, and a driver's seat belt (DSB) signal and a passenger'sseat belt (PSB) signal which indicate the use of driver and passenger(s)seat belts, respectively.

MCU 20 processes the various input signals, as will be explainedhereinafter, and produces a rollover deployment command signal 56, whichis indicative of a detected vehicle rollover condition. In addition, MCU20 provides the detected rollover deployment command signal on line 18to control designated onboard control devices, such as a seat beltreeler control 34, a seat belt pretensioner control 36, and a seat beltretractor control 40. Seat belt reeler control 34 controls the seat beltreeler for both the driver's side and passenger's side via respectivesignals DREL and PREL, as provided on output signals 44 and 46,respectively. Seat belt pretensioner control 36 likewise controls seatbelt pretensioning for the driver's side and passenger's side viasignals DPRET and PPRET, as provided on output lines 48 and 50,respectively. A diagnostic current source and sink 38 allows fordiagnostic testing of the seat belt reeler control 34 and seat beltpretensioner control 36. The seat belt retractor control 40 controlsretractor locks associated with the seat belt to both the driver's seatbelt and passenger's seat belt via signals DRET and PRET, as provided onoutput lines 52 and 54.

The rollover detection apparatus of the present invention is furthershown in FIG. 2. Included are anti-aliasing filters 60 a-60 c coupled tothe output of each of angular rate sensor 12, vertical accelerometer 14,and lateral accelerometer 16, respectively. The anti-aliasing filters 60a-60 c each employ a low-pass filter to remove high frequency signalcontent, thereby eliminating at least some corruption of the sensedsignals. The rollover detection apparatus includes a rollover detectionalgorithm 58 for generating a rollover deployment decision as a functionof the filtered angular rate signal and the vertical accelerationsignal. An arming algorithm 65 is also shown receiving the verticalacceleration signal and the lateral acceleration signal. The armingalgorithm serves as a redundancy check prior to deploying devices duringa rollover event, as is known in the art. This may be achieved byemploying an arbitration block 68, which may include a logic AND gatefor logically ANDing the arming signal with the rollover deploymentdecision. The output of the arbitration block 68 provides the rolloverdeployment command signal 56. It should be appreciated that theanti-aliasing filters 60 a-60 c, rollover detection algorithm 58, armingalgorithm 65, and arbitration block 68 may be implemented in softwareprocessed by the MCU 20. Further, the arbitration block 68 may receiveother possible signals, such as resets, overrides or false indicators,if desired, and may control the rollover command signal 56 based onthese signals.

Referring to FIG. 3, the rollover detection algorithm 58 is shown fordetecting a vehicle rollover about the longitudinal axis of the vehicle.The rollover detection algorithm 58 is preferably implemented insoftware that is stored in read-only memory (ROM) internal to the MCU20. However, it should be appreciated that the algorithm for detecting arollover condition of a vehicle according to the present invention canbe implemented with analog circuitry and/or digital processing. Itshould also be appreciated that while a vehicle rollover condition aboutthe longitudinal axis of the vehicle is detected by the rolloverdetection algorithm, the algorithm can likewise be used to detect avehicle pitchover about the lateral axis of the vehicle by sensing pitchangular rate in place of the roll angular rate.

The vehicle rollover detection algorithm 58 receives the sensed angular(e.g., roll) rate signal {dot over (φ)} generated by the roll angularrate sensor 12, and further receives the sensed low-g verticalacceleration signal generated by the vertical accelerometer 14, andprocesses the roll rate signal and vertical accelerometer signal togenerate a vehicle rollover deployment decision. The angular rate sensor12 supplies a signal proportional to the rate of angular rotation aboutthe sensing axis, such as the roll rate about the longitudinal axis ofthe vehicle. With conventional angular rate sensors, the sensed ratesignal typically includes a non-zero bias, even when the vehicle is atrest, which can falsely indicate the presence of a roll rate. Inaddition, the non-zero bias can change significantly with thetemperature of the roll rate sensor 12, and can further drift in valueas the sensor ages.

The rollover detection algorithm 58 employs an adaptive bias removalwith output minimum (ABROM) logic 62 for eliminating bias and furtherreducing noise associated with the sensed angular rate signal. The ABROMlogic 62 effectively removes constant and slowly-varying offset bias, aswell as small amplitude signals, thereby eliminating spurious noise andlow level non-rollover signals, such as may occur on rough roads orduring abusive vehicle driving conditions. The rollover detectionalgorithm preferably employs the ABROM logic 62 as is described laterherein in greater detail in connection with FIGS. 8-10.

Referring briefly to FIG. 4, the various regions of operation for oneexample of an amplitude response of the ABROM logic 62 is illustratedtherein. The sensed angular rate input signal {dot over (φ)} is dividedinto separate regions that determine the angular rate output signal {dotover (φ)}. The ABROM logic 62 produces an output signal {dot over (φ)}set equal to zero when the angular rate input signal is below a minimumvalue, which defines an output minimum region, as is shown by line 72.The minimum value may be equal to ± five degrees/second, according toone example. When the angular rate input exceeds the output minimumvalue, the ABROM logic 62 output signal is substantially linear throughthe all-pass filter region and substantially linear for signals withfrequency content substantially higher than the cut off frequency of thehigh-pass filter through the high-pass filter regions as shown by lines70 and 74. The high-pass filter region removes low-level constant orslowly varying signals from the output rate signal. According to oneembodiment, the high-pass filter has a very low cut off frequency (e.g.,0.1 Hz) to remove the effects of thermal drift and aging of the sensor.

The all-pass filter region eliminates bias for high amplitude signalsduring which the likelihood of a rollover event is more likely to occur.The all-pass filter region passes the input rate {dot over (φ)} to theoutput with bias removed, but without filtering. Thus, with larger levelsignals, such as may occur during a rollover event, there is no delay orattenuation of the angular rate output signal {dot over (φ)}. Theoperating regions are integrated to provide smooth operation over theentire operating range to reduce imperfections in the angular ratesensor, so that the resulting algorithm results achieve enhancedreliability.

Referring back to FIG. 3, the rollover detection algorithm 58 employs anintegrator 64 with intelligent drift removal for computing a vehicleaccumulated roll angle φ 62 based on the angular roll rate history. Theintegrator 64 preferably includes an infinite impulse response (IIR)integrator that performs backward integration, which should be readilyapparent to those skilled in the art. The integral (roll angle φ) ismonitored and adjusted periodically to remove biases that may havecorrupted the signal, as explained herein. The dynamics of thisintegration provides immunity to remaining sensor biases, noise, andnon-rollover events, while providing for adequate detection of slowrollover events and two-step rollovers that may be encountered invehicle usage.

The rollover detection algorithm 58 further includes deployment logic 66with gray-zone duration indicator and near-rollover immunity whichprocesses the roll angle φ and the sensed and processed angular rate{dot over (φ)}, and generates a rollover deployment decision. Thecombination of the roll angle φ and the processed angular rate signal{dot over (φ)} are compared against two threshold curves to determinewhether or not to generate the rollover deployment signal 56. If thecombination of roll angle φ and angular rate signal {dot over (φ)}exceeds an upper curve, deployment is commanded. If the combination ofroll angle φ and angular rate signal {dot over (φ)} is less than a lowercurve, deployment is never commanded. However, if the combination of theroll angle φ and rate signal {dot over (φ)} is between the upper andlower curves, within a gray-zone, the deployment logic 66 monitors thesignal duration within the gray-zone and dynamically adjusts the uppercurve relative to the lower curve, to allow for timely deployment oncertain vehicle maneuvers. The deployment logic 66 further monitors thedynamics of the vehicle to detect driving conditions where anear-rollover event may occur, and provides rollover deployment immunityto certain detected near-rollover events. For example, when a vehicleapproaches, but does not exceed, the vehicle static stability roll angleand quickly drops back to level ground, the deploy logic 66 may adjustthe minimum deploy angle at which deployment is allowed to provideimmunity to such near-rollover events. Additionally, deployment logic 66may adjust the deployment requirements for rollover events occurring indifferent directions, e.g., clockwise versus counterclockwise rotations,of the vehicle.

Integrator with Intelligent Drift Removal (IIDR)

The integrator 64 with intelligent drift removal computes the vehicleroll angle φ based on the angular roll rate {dot over (φ)} history bycontinuously backwards integrating, with an infinite impulse responseintegration, the measured angular roll rate {dot over (φ)}. The measuredangular roll rate is sampled at regular time intervals (e.g., i-2, i-1,i, etc.), and an unlimited number of roll rate samples may be includedin the integration. The integrator 64 further adjusts the roll angle φto remove bias and monitor vertical acceleration and controls the rollangle adjustment based on a determined vehicle inclination angle.

While the ABROM logic 62 removes slowly-varying biases typically presentin automotive-grade angular rate sensors, practical implementation ofcontrol algorithms and lower cost fixed point microprocessors generallymust accommodate further sources of error. In fixed point mathematics,there typically exists a limited number of bits of resolution madeavailable. As a consequence, the numeric representation of signals(variables) generally must be balanced by trading off between theavailable range and the smallest resolution of the variable. Generallyspeaking, the wider the range allowed, the larger the minimum resolutionof the variable must be. For variables with wide dynamic ranges, such aswith the angular rate signal, the larger required range implies a lowerlimit on the resolution. Thus, affordable low-cost microprocessors offerless processing bits, and thus the resolution is also generally poorer.Because of the limited resolution, a difficulty arises when integratingthe angular rate signal to determine roll angle, and there willtypically be small errors on every signal. Since the process ofintegration is a summing operation, these small errors can compound overtime. Over a sufficiently long period of time, the compounded errorscould add up to an appreciable error in the roll angle signal. It shouldalso be appreciated that other sources of noise and error can alsocontribute in a similar way to the roll angle errors. Accordingly,inherent errors in the microprocessor can conspire to create error inthe signal processing.

The present invention achieves a low-cost rollover detection apparatuswhich adjusts the integral periodically to remove the biases that mayhave corrupted the signal, and thus allows for use of a minimal numberof sensors and an affordable controller. The rollover detectionapparatus further monitors vertical acceleration over a long period oftime and determines if the vehicle is at a significant inclinationangle. If the vehicle is at a significant inclination angle, adjustmentof the roll angle is suspended. Thus, the use of the verticalacceleration signal to suspend the roll angle adjustment provides anadaptive method to preserve legitimate signals that factor in aninclination angle of the vehicle, such as when the vehicle is travellingon a sloped roadway for a significant period of time. This may beespecially true when the vehicle is driving off-road on hilly terrain.

Referring to FIGS. 5A and 5B, a routine 100 is illustrated forperforming the integration of the angular rate signal {dot over (φ)} toproduce the roll angle φ and adjusting the roll angle to eliminate bias,while suspending the adjustment when a long-term inclination angle ofthe vehicle is detected by the vertical accelerometer. The routine 100starts at step 102 and proceeds to step 104 to measure the angular rateinput received from the ABROM logic 62. Next, in step 106, routine 100performs a mathematical integration of the measured angular rate signalto produce a roll angle at current time step i. The integration computesthe product of the current rate (i) and loop time and sums the productwith the previous integration values for times i-1, i-2, etc. Theintegration process is a backward integration, which should be evidentto those skilled in the art.

Following integration step 106, routine 100 proceeds to step 108 toincrement a bias counter. Next, the roll angle is compared to zerodegrees in decision steps 110 and 112. If the roll angle is greater thanzero degrees in step 110, routine 100 proceeds to increment a biasgreater than (GT) counter in step 114. If the angle is less than zerodegrees, routine 100 proceeds to increment a bias less than (LT) counterin step 116. Following either of the increment steps 114 or 116 or ifthe angle is equal to zero degrees, routine 100 proceeds to decisionstep 118 to check if the bias counter has exceeded an adjust periodlimit having a predetermined time value, such as twenty (20) seconds,which establishes the long-term time period for detecting the vehicleroll inclination angle. In effect, the bias counter acts as a timer,such that if the time limit has not been reached, then control isreturned to the top of the control routine 100.

By comparing the roll angle to the level ground value of zero degrees indecision steps 110 and 112, it is assumed that the vehicle returns to aroll angle of approximately zero degrees over a sufficiently long periodof time. By using this assumption, the rollover detection is valid overa very wide range of driving scenarios without requiring additionalsensors and hence cost to the rollover detection apparatus.

If the bias counter exceeds the adjust period, the vertical accelerationA_(Z) of the vehicle is measured in step 120 and is further low-pass lagfiltered in step 122. The low-pass lag filter provides low-passfiltering with coefficients designed to remove short-term variations androad noise. A typical low-pass lag filter delay in the range of about0.3 to 5.0 seconds may be employed. The filter delay should be shorterthan an adjust period. The low-pass lag filtered acceleration input isthen compared to the summation of a nominal value and an offset value indecision step 124, in order to determine if the vehicle is currently ata roll inclination angle sufficiently rotated away from a level groundof zero degrees. The nominal value is the expected value during leveldriving of the vehicle, and may include a typical value of −1 g (i.e.,9.8 meters/second/second) representing the acceleration of gravity onthe surface of the Earth. Alternately, a built-in nominal value of 0 gmay be employed with the nominal value. The offset value is theworst-case limit of all sensor errors, including the summation ofmanufacturing tolerances, temperature effects, aging effects, and othernon-signal related biases. The magnitude of the offset value may includea typical value in the range of about 0.5 to 0.01 g. However, it shouldbe appreciated that further refinements in sensors or bias compensationmay further reduce the offset value.

If the value of the filtered low-g vertical acceleration A_(Z) is lessthan the summation of the nominal value and the offset value, it isdetermined that the vehicle is not at a significant roll inclinationangle, and routine 100 proceeds to provide an adjustment to the rollangle. To provide adjustment to the roll angle, routine 100 checks forwhether the bias LT counter is greater than one-half of the adjustperiod in decision step 126. If the bias LT counter is greater thanone-half the adjust period, the roll angle is adjusted to be increasedby an angle adjust value in step 128. If the bias LT counter is notgreater than one-half the adjust period, routine 100 proceeds todecision step 130 to check if the bias GT counter is greater thanone-half the adjust period and, if so, adjusts the angle to subtract theangle adjust value. Following either adjustment in steps 128 and 132, orin a case where both the bias GT counter and the bias LT counter do notexceed half of the adjust period, the counter is reset in step 134, andcontrol then passes back to the top of the control loop.

If the filtered value of the low-g vertical acceleration is greater thanor equal to the summation of the nominal value and the offset value, asdetermined in decision step 124, routine 100 determines that the vehicleis positioned at a significant roll inclination angle. If the vehicle isdetermined to be positioned at a significant roll inclination angle,routine 100 performs no adjustment to the roll angle and, instead,proceeds directly to step 134 to reset all of the counters to zero.Following step 134, routine 100 returns to the top of the control loop.

Accordingly, the integrator 64 with intelligent drift removal and itscontrol routine 100 monitors and adjusts the roll angle φ periodicallyto remove biases that may corrupt the roll angle signal when thefiltered vertical acceleration A_(Z) is less than the summation of thenominal and offset values. Whenever the filtered vertical accelerationA_(Z) reaches the summation of the nominal and offset values, indicativeof a long-term significant roll inclination angle experienced by thevehicle, the periodic bias adjustment is prevented. Thus, thesignificant roll inclination angle is factored into the roll angle andis used to anticipate an upcoming rollover event of the vehicle. Bypreventing further adjustment of the roll angle while the vehicle isexperiencing a significant roll inclination angle, legitimate roll anglesignals are preserved and are compared to the deploy threshold curve todetermine the rollover deployment decision. This results in an adaptiveroll angle adjustment.

The implementation of the decay is highly efficient in microprocessorresources. The use of the filtered vertical accelerometer signal A_(Z)to suspend the adjustment provides an adaptive method to preservelegitimate signals that may be important to proper functioning of therollover deploy command. Accordingly, the vertical accelerometer detectsa significant roll inclination angle and prevents adjustment to theintegration output angle, while preserving bias removal as long as thevehicle is not experiencing any significant roll inclination angle. Thevertical acceleration signal A_(Z) is low-pass filtered so as to removehigh frequency signals. Thus, the filtered vertical acceleration signalprovides a long-term average value indicative of the vertical forcesapplied to the vehicle relative to the orientation of the vehicle.During a normal level driving condition, the vertical force would beequal to gravity on the surface of the Earth which is approximately 9.8meters/second/second. When the sensed vertical acceleration valuediffers to a lesser value, it is assumed that the vehicle is oriented onan incline. The amount of force generated can be represented by a cosineof the angle of inclination multiplied by the Earth's gravitationalforce. While a vertical accelerometer is shown and described herein fordetermining a vehicle roll inclination angle, it should be appreciatedthat other sensors may be employed to provide an indication of theinclination of the vehicle, without departing from the teachings of thepresent invention.

Deployment Logic with Gray-Zone Duration Indicator

The deployment logic 66 with gray-zone duration indicator andnear-rollover immunity generates a rollover deployment signal based onthe roll angle φ and sensed angular rate {dot over (φ)} output from theABROM logic 62. Referring to FIG. 6, one example of a gray-zone 150 isillustrated therein. The deployment logic 66 compares the sensed angularrate {dot over (φ)} and the roll angle φ against two threshold curves,namely an all-deploy (upper) curve (line) 156 a, beyond which adeployment is always commanded, and a no-deploy (lower) curve (line) 156i, below which a deployment is never commanded. The region between thesetwo curves is termed the gray-zone 150. The deployment logic monitorsthe signal duration within the gray-zone 150, and dynamically adjuststhe all-deploy curve closer towards the no-deploy curve. This allows fortimely deployment on corkscrew and other events involving complexvehicle motions, while a decay factor provides immunity to thresholdnon-trigger events, such as ramp jumps or off-road driving conditions.

The vertical axis of the gray-zone duration indicator is theinstantaneous value of the angular roll rate {dot over (φ)} followingprocessing by the ABROM logic 62. The horizontal axis is the currentvalue of the roll angle φ, as determined by the integrator 64. Forconvenience of description herein, both roll rate {dot over (φ)} androll angle φ are considered as absolute values, however, in general,these values can be either positive or negative numbers. It should alsobe important to appreciate that clockwise and counterclockwise rolloversmay have different requirements, and therefore may employ separatecalibrations with minor changes to the deployment logic and an increasein the number of adjustable parameters.

The curvaceous paths illustrated in FIG. 6 represent the trace ofpairwise points (angle φ, rate {dot over (φ)}) for severalrepresentative rollover and near-rollover events. Paths 160 shownon-rollover events, while paths 170 and 172 show rollover events. Onthe horizontal axis, representing the current roll angle value φ, is thestatic stability angle 180 which is the roll angle at which the vehicleis perfectly balanced on two wheels (on the same side of the vehicle),and any further increase in angle will result in the vehicle tippingover onto its side. For a typical passenger vehicle, the staticstability angle 180 for rollovers may range from forty-six (46) toseventy (70) degrees, depending on the vehicle. On the vertical axis,representing the roll rate {dot over (φ)}, is the impulse rollover rate182 which, when applied at an angle of zero degrees, will cause thevehicle to pass through the static stability angle and rollover. Betweenthe two extreme values 180 and 182, and typically lower in magnitude, isthe all-deploy line (curve), such as line 156 a, which represents pairsof angle and rate, such that any pair of angle and rate on or above theall-deploy line will nominally indicate a deploy condition. Theall-deploy line is shown here as a straight line, however, considerationof the vehicle suspension dynamics and other non-idealities in thevehicle structure may conspire to make this boundary a complex shape.The shape and slope of this line may also depend on additional inputsignals, such as vertical or lateral acceleration signals. However, forsimplicity of discussion, the all-deploy line is assumed to be linearand of a single slope. It should be noted that the current inventionextends to arbitrary complex shapes of the all-deploy line, withoutdeparting from the spirit of the present invention.

Within the gray-zone 150, pairwise points of rate and angle may involveeither rollover events which have not yet accumulated sufficient energyto rollover, or very severe non-rollover events. The gray-zone 150 isconsidered an arbitrarily fine line between deploy and non-deployevents. Factors such as vehicle-to-vehicle variation and manufacturingtolerances in components require a degree of separation between theall-deploy and no-deploy events when calibrating the rollover detectionalgorithm.

The gray-zone 150 is limited at or away from the axes to provideimmunity against pairs of angle and rate that may instantaneously exceedthe all-deploy line, but are of insufficient severity to command adeployment. The left boundary 152 of the gray-zone 150 is defined by aminimum roll angle lower limit required before allowing a deployment.The bottom boundary 158 of the gray-zone 150 is defined by a minimumangular roll rate at which the rollover detection algorithm will beallowed to deploy the rollover decision, and is used to preventdeployment on very slow roll events, such as roll experienced in aparking lot sink hole. The minimum roll angle 152 and roll rate 158 arecalibratible parameters that are set in the rollover detectionalgorithm.

Vehicle events causing the angle and rate pair to spend an appreciableamount of time within the gray-zone 150 are given special consideration.In crash events, the vehicle may undergo complex motions beforeeventually rolling over. The ability to dynamically adjust theall-deploy line is allowed if the time duration within the gray-zone 150is appreciable. For these types of events, the gray-zone time durationis used to lower the all-deploy line closer to the no-deploy line. Thelonger the time duration within the gray-zone, the more likely the eventwill trigger deployment of safety devices.

The minimum deploy angle has a lower bound limit shown by line 152,which serves as the default limit. During normal vehicle operation, theminimum deploy angle is set at the minimum limit 152. During certainnear-rollover events, the minimum deploy angle is increased by delta Δto line 152 a so as to prevent the deployment of a rollover commandsignal during the near-rollover event. When the near-rollover event haspassed and the vehicle returns to a normal operation, the minimum deployangle returns to the minimum limit default setting on line 152.Accordingly, by shifting the minimum deploy angle to line 152 a, severeevents which cause a near-rollover, but are short of a rollover event,may be prevented from triggering the deployment of a rollover commandsignal, especially during the impact associated with the return to alevel surface.

The deployment logic 66 processes the integrated angle φ and the angularrate {dot over (φ)} with logic that indicates whether these signals, incombination, are indicative of an anticipated rollover event, preferablysufficiently prior to an actual rollover occurrence. In many schemes, inorder to make the rollover detection algorithm sensitive enough todetect a rollover condition during the early stages of such an event,there is the risk that the rollover detection algorithm may deploy therollover decision on certain non-rollover events of sufficient severity.One example is the return of the vehicle to a level fall from anear-rollover event, as explained below.

A vehicle can be characterized by the static stability angle, which isthe roll angle at which the vehicle center of mass is directed above theline between two tires on the same side of the vehicle, which istypically about forty-five (45) to seventy (70) degrees, depending onthe type of vehicle. Under certain driving conditions, a vehicle maysustain an increased roll angle to nearly that of the static stabilityangle, without triggering the rollover deployment command signal. If oneside of the vehicle ramps upward, once the vehicle is rolled nearly tothe static stability angle, the vehicle may suddenly drop back to asubstantially level surface. This drop may develop a large velocity onthe downward returning side of the vehicle and, when the vehicle impactsthe ground, the sensors may record a very severe event. In effect, thevehicle may be slammed onto the suspension hard enough to travel to thehard bumper stops of the vehicle, possibly even rotating further as thetires compress and the vehicle suspension flexes. This over travel canamount to ten degrees or more of rotation opposite to the originalclimbover, and is associated with high angular rates and large values ofacceleration in both the lateral and vertical directions. Since avehicle rollover did not occur in this near-rollover scenario, it wouldbe appropriate for the rollover detection apparatus not to deploy arollover command signal. In accordance with the present invention, theminimum angle at which deployment is allowed is adjusted so that therollover detection is immune to these types of near-rollover events.

Referring to FIGS. 7A and 7B, the deployment logic routine 200 isillustrated for adjusting the minimum deploy line and adjusting theall-deploy line based on a gray-zone time duration. Deployment logicroutine 200 starts at step 202 and proceeds to step 204 to determine theangle input processed by the integrator 64. Next, a low-pass lag filteris applied to the angle in step 206, such that the angle signal isdelayed by a time period of about 0.3 to 0.5 seconds. Thus, the low-passfilter may be designed with a group delay in the range for signals withfrequency content from about 0.01 Hz to 2.0 Hz. The low-pass filteringalso prevents false triggering based on short-term spikes which mayoccur in the integration output angle.

In step 208, deploy logic routine 200 computes value delta Δ which isdefined as the difference of the absolute value of the instantaneousangle subtracted from the absolute value of the difference between theinstantaneous angle value and the group delayed (filtered) angle. Thus,the calculation of delta Δ achieves a value which is only positive ifthe group delayed angle is one polarity and the instantaneous angle isan opposite polarity, and only when this difference exists overdurations shorter than the group delay time period.

Next, in decision step 210, routine 200 checks whether delta Δ isgreater than a pre-specified delta max limit, and if so, sets delta Δequal to the delta max limit in step 212. Following steps 210 and 212,routine 200 proceeds to check if delta Δ is greater than zero and, ifso, sets the minimum deploy angle equal to the minimum deploy angleincreased by delta Δ in step 216. Otherwise, the minimum deploy angle isset equal to the minimum deploy angle lower limit in step 218. Thus, ifthe vehicle is at a roll angle at the current time instant, but was atzero roll angle very recently, then delta Δ will be equal to a value ofzero. If the vehicle has a roll angle that has been increasing steadilyover a duration comparable to the group delay time of the filter, thendelta Δ will be negative. So, if delta Δ is zero or less, the minimumdeploy angle is set to the default minimum value. However, if delta Δ ispositive, indicating that the vehicle is returning from a near-rollovercondition, then the value of delta Δ is added to the default minimumvalue to determine the current setting of the minimum deploy angle.Thus, for a time period such as 0.3 to 0.5 seconds following anear-rollover event, the minimum deploy angle will increase temporarily,thereby giving additional immunity against this severe, but non-rolloverevent.

Following adjustment of the minimum deploy line, the deployment logicroutine 200 proceeds to the steps shown in FIG. 7B to adjust theall-deploy line based on the gray-zone time duration. In decision block220, deployment logic routine 200 checks if the two following conditionsare met: (1) the angular rate is above the minimum rate value; and (2)the computed roll angle is above the minimum angle value. For clarity,only positive values are considered herein, but the concept is equallyvalid for negative values and negative rates. Next, in decision step222, deployment logic routine 200 checks for whether the pairwisecombination of roll angle and rate exceeds the all-deploy line. If theall-deploy line is exceeded, then decision step 224 checks if the rollangle has actually been increasing since the previously iterationthrough the deployment loop. This concept of using previous iterationsto look for an increasing angle may be extended to include a weightedsum of several prior samples of the roll angle φ. Provided the rollangle φ has been increasing, a rollover deployment decision is generatedin step 226. Otherwise, routine 200 proceeds to decision step 228.

The check provided in step 224 ensures that deployment will only becommanded at a point in time when the roll angle φ is actuallyincreasing towards the rollover point. In addition, this check providesadditional immunity against a class of vehicle motions where asubstantial angle has already been accumulated, and then the vehicleexperiences a sharp angular rate in the opposite direction. Without thischeck, such a non-rollover driving scenario could possibly lead to aninadvertent deployment. In an embodiment where separate calibrations areused for clockwise and anti-clockwise rollovers, the logic which checksfor whether the roll angle is increasing instead becomes a check toverify that the roll angle and the roll rate are of the same sign.

If the pairwise combination of roll angle and roll rate is below thecurrent all-deploy line, or if the roll angle is not increasing, thendecision step 228 checks for whether the roll angle and rate pair varieswithin the gray-zone, by being above the no-deploy line. If the angleand rate pair is within the gray-zone, then the duration counter isincremented in step 230, and the all-deploy line is adjusted in step 232based on the duration count. Adjusting the all-deploy line based on theduration count of the roll angle and rate pair being within thegray-zone provides timely deployment for a wide range of rolloverevents. In scenarios where the rollover is initiated suddenly, evenviolently, such as a lateral curb trip or a lifting knock-over impact,the roll angle and rate pair will rise rapidly, and quickly surpass theall-deploy line. However, during rollovers involving complex motions,such as a corkscrew, certain fallovers, rollovers during off-roaddriving, or concatenated events leading up to a rollover, the vehiclemay hover briefly, or undergo auxiliary impacts before reaching acritical point requiring deployment. If the vehicle attitude moveswithin the gray-zone momentarily, but then returns to a substantiallylevel position, no deployment is typically required. However, a moresustained duration within the gray-zone may also indicate a severe eventin progress and, in such cases, when the vehicle motion finally advancesinexorably towards rollover, deployment is often required without delay.To accomplish these goals, the gray-zone duration indicator willgradually reduce the all-deploy line, such as from line 156 a to line156 b or further to any of lines 156 c-156 h, thereby effectivelycollapsing the gray-zone to allow this class of events to achieve atimely deployment when needed.

Adjustment of the all-deploy line may be regarded as a linearinterpolation of the end points of the all-deploy line towards theno-deploy line. Each advance of the all-deploy line closer to theno-deploy line is made based on the duration of the angle and ratepairwise samples being within the gray-zone. A sufficiently longduration within the gray-zone will eventually command a deployment. Therate of advance of the all-deploy line towards the no-deploy line is anadjustable or calibratible parameter of the algorithm. According to oneexample, three to five samples within the gray-zone are required beforethe all-deploy and no-deploy lines coincide. While a linear straightline interpolation is described herein, the present invention alsoextends to non-linear interpolation, and piece-wise linear boundaries ofthe gray-zone. Adjustment of the all-deploy line should be reset back tothe original default value, after a near-rollover event concludes.

If the pairwise combination of roll angle and angular rate is determinednot to be above the no-deploy line as determined in step 228, controlpasses to decision step 234 to check if the duration count is greaterthan one. If the duration count does not exceed one, then routine 200proceeds to set the all-deploy line in step 232. Otherwise, if theduration count exceeds a value of one, routine 200 increments the decaycount in step 236, and then proceeds to decision step 238 to check ifthe decay count is greater than a decay count maximum value. Once thedecay counter reaches a preset maximum count, then the duration count isdecremented in step 240, and the all-deploy line is adjusted based onthe duration count in step 232. The purpose of the decay count is topreserve the duration count for a brief period of time should thevehicle motion pass out of the gray-zone momentarily. The decay countmaximum value is set so that concatenated events receive a timelydeployment, while rough road or near-rollover events with only periodicexcursions into the gray-zone receive immunity offered by the defaultall-deploy threshold. After the adjustments have been made to theall-deploy line, control is returned to step 204 for the next loop ofsample iterations for routine 200.

Accordingly, the deployment logic 66 provides a variable threshold forcomparison with the roll angle to determine whether to deploy a rolloverdecision. The variability of the rollover threshold allows for thetimely detection of certain vehicle driving events so as to predict inadvance an upcoming rollover event. The variable threshold furtherallows for the detection of very near-rollover events which fall shortof an actual rollover event, so that the rollover detection does notproduce a rollover decision.

Adaptive Bias Removal with Minimum Output (ABROM) Logic

The ABROM logic 62 processes digitally sampled input signals in such away that constant or slowly-varying biases are removed, small noisesignals are eliminated, and large-amplitude signals are passed with anadjusted bias to achieve signals with optimal accuracy. The ABROM logic62 is particularly useful for processing signals sensed via an angularrate sensor for use in the rollover detection apparatus of the presentinvention. However, it should be appreciated that the ABROM logic 62 isalso useful for processing signals generated by other sensing devicesfor use in various applications, without departing from the teachings ofthe present invention.

The ABROM logic 62 has three primary regions of operation according tothe embodiment shown. These three primary regions of operation are shownin FIG. 4. In the high-pass filter region, for small amplitude signalsbelow an adaptive threshold, a high-pass filter is applied. In theall-pass region, for larger amplitude signals above the adaptivethreshold, the signals are passed unchanged, except for the removal ofthe most recent bias estimate, which is derived from the high-passfilter. If the output of the high-pass filter is below a minimum outputlevel, then the output is forced to zero in an output minimum region.

The operation of the ABROM logic 62 provides a number of benefits byproviding removal of static or slowly moving bias from a sensorgenerated signal. The minimum output function further provides forfaster recovery from drifting input values, as compared to traditionalfilter approaches. The all-pass region above the adaptive thresholdcorrects for sensor biases, but otherwise passes the input signal to theoutput. This avoids filter delays associated with digital filters, andavoids attenuation of low-frequency components of the signal above theadaptive threshold. The ABROM logic 62 is applicable to systems whichare monitored for intermittent, asynchronous signals, especially wherebias or offset changes are poorly tolerated. For rollover detectionalgorithms, especially those which use integration of a sensor generatedsignal, the ABROM logic 62 allows for rapid response times with minimalerrors.

Referring to FIG. 8, an ABROM control routine 300 is illustratedtherein. Routine 300 begins at step 302, and in decision step 304 checksif the angular rate sensor (ARS) input is greater than an adaptivethreshold. The absolute value of the input may be used, or differentthresholds can be used on either side of zero, if desired. The checkperformed in decision step 304 reduces microprocessor processing timewhen a signal excursion above the adaptive threshold occurs. These areevents intended to be detected or measured, and once such events begin,the signal should be processed as rapidly as possible.

When the first signal sample exceeds the adaptive threshold, a runningbias is fixed and stored until the signal amplitude drops below theadaptive threshold. This is achieved by checking if the first sample isabove an adaptive threshold in step 306 and, if so, capturing a runningbias equal to the difference of the input (i-1) minus the output (i-1)in step 308. Otherwise, if the first sample is not above the adaptivethreshold, in step 310 the ABROM output is set equal to the differenceof the input minus the running bias. The running bias is computed bysubtracting the input signal from the high-pass filter output at themost recent prior time step. The frequency response of the high-passfilter is such that constant or slowly varying biases are removed fromthe input such that the high-pass filter output is at or near thenominal zero value (in the absence of large-amplitude signals).

The ABROM logic is particularly useful for situations where the signalsof interest are of relatively large amplitude and of relatively briefduration, as compared to the time constant of the high-pass filter. Inthese cases, the running bias is a good approximation of the true bias.The longer the duration of such excursions, the more error that canoccur by using the running bias. While prior signal excursions above theadaptive threshold could cause the running bias to vary from the truebias, two methods are used to minimize these affects, namely, (1)reinitalizing the high-pass filter after a large amplitude excursion;and (2) using the output minimum, as described below.

Samples above the adaptive threshold (an absolute value) are passedwithout attenuation or delay, but are corrected by subtracting off therunning bias, so that low-frequency components of the large amplitudesignals will be accurately reflected in the output. For input signalswhich do not exceed the adaptive threshold, routine 300 proceeds to step312 to check if the first sample is below the adaptive threshold. Whenthe first sample is below the adaptive threshold, the filter isinitalized with the running bias in step 314, before proceeding todecision step 318. However, if the first sample is not below theadaptive threshold, high-pass digital filtering is performed in step316, prior to proceeding to decision step 318. Decision step 318 checksif the filter output is below a minimum output and, if not, routine 300returns to step 304. However, if the filter output is below the minimumoutput, then routine 300 proceeds to step 320 to set the ABROM outputequal to zero, prior to returning to step 304.

The running bias is the best estimate of the true bias, although it maychange slightly for the duration of the signal excursion. By using therunning bias as a starting point for the high-pass filter, the onlyerror that the high-pass filter needs to correct for is the small amountof bias shift that may have occurred during the brief signal excursionabove the adaptive threshold, thereby necessitating the need to correctthe full amount of the bias upon initalization at a zero value beforeexperiencing significant overshoot if the filter was used for the entiresignal excursion.

It is preferred that the high-pass filter be a first order IIR filter,such as a Butterworth filter. However, the ABROM logic can be applied tofilters of any order, by using successive time steps to initializesuccessive terms of the digital filter. Reinitializing the filter withthe running bias effectively starts up the filter where it left off atthe start of the signal excursion above the adaptive threshold. Any biasshift which occurred, or signal attenuation below the adaptivethreshold, is all that remains for the high-pass filter to remove. Sincethe shifts are small, in general, the recovery is much more rapid thantraditional high-pass filters.

The recovery time can be reduced with a minimum output processingtechnique, as described as follows. The intermediate output of the ABROMlogic is either the high-pass filter output or the bias-adjusted signalif the input is greater than the adaptive threshold. If the output fallsbelow a minimum output level, the output is set identically equal tozero. This operation allows fast recovery from any extended periods oflarge-amplitude inputs and reduces errors when the ABROM output isintegrated, such as for rollover sensing.

FIG. 9 illustrates the results of the ABROM logic for removing bias whenthe bias drifts up rapidly to a high value, resides at the high valuebriefly, then drifts back to zero, according to one example. The solidline 330 represents the input to the ABROM logic, and the dashed line332 represents the output. At the early rise levels, the output 332remains at zero according to the minimum output function. As the inputsignal 330 continues to rise, the output 332 begins to be attenuatedaccording to the functioning of the high-pass filter, demonstratingasymptotic behavior up to the plateau of the input signal 330 at a timeperiod of about fifty (50) seconds. When the bias remains at the highlevel, the high-pass filter causes the output to decay towards zero,until the output 332 falls below the minimum output, and then dropsimmediately to zero. This demonstrates a fast recovery time. When theinput 330 begins to fall, at about 100 seconds, the same behavior isexhibited, except in the reverse polarity. Accordingly, the downwardramp of the input signal 330 is greater than the input ramp, leading toa higher output 332 deviating from zero. Accordingly, the bias removalof the ABROM logic does not come at the expense of signal fidelity forlarger amplitude signals as described below.

Referring to FIG. 10, a large amplitude signal excursion is shownsuperimposed on a constant bias. The constant bias is set to a rate ofapproximately minus ten (−10) at which point the ABROM logic isinitalized. The signal excursion occurs at about forty (40) seconds, andhas a peak amplitude rate of about sixty (60), referenced to the bias.The maximum signal level is reached within about two seconds, and thenhas a plateau for several seconds, before ramping back down to the biaslevel. According to this example, the adaptive threshold limit is set toa value of about twenty (20), and the minimum output level is set to avalue of about two (2). The solid line 340 represents the input signaland the dashed line 342 represents the output. At time equals zero, theoutput 342 initalizes to the first signal at a value of about minus ten(−10), but then corrects toward a zero value with a time constantcharacteristic of the high-pass filter. At approximately twenty-one (21)seconds, the output 342 (an absolute value) drops below the minimumoutput, and the output 342 goes to zero. When the signal excursionbegins at thirty-five (35) seconds, the output begins to climb andexactly matches the input signal except for the shift equal to therunning bias. The running bias is the instantaneous difference betweenthe input 340 and the output 342 at the moment the signal exceeds theadaptive threshold. The running bias is held fixed until the signalreturns below the adaptive threshold.

It is important to note that there is substantially no signal distortionduring the plateau of the input signal around forty (40) seconds. Whenthe signal returns back below the adaptive threshold, the running biasis used to initialize the high-pass filter. There may still be somerecovery needed, because of the action of the high-pass filterattenuating the signal as it begins to climb, but before the adaptivethreshold has been reached. This overshoot can be further reduced bycalculating the running bias at the sample point further back in time,assuming there is no history of other events. As an option, the runningbias can be computed at any time point in the past, or an average ofsuch points, for according to logic which detects the presence/absenceof the previous signal history. While the ABROM logic is shown anddescribed herein in connection with the rollover detection apparatus, itshould be appreciated that alternate bias removal logic may be employedwithout departing from the teachings of the present invention.

The rollover detection algorithm as described herein provides enhancedfunctionality over a wide range of rollover events, while using a smallnumber of sensors. The integrator 64 with intelligent drift removal anddeploy logic 66 having near-rollover immunity described herein provideflexibility to ensure timely deployment on rollover events, and adequateimmunity to non-rollover and near-rollover events. The performance ofthe rollover detection provides enhanced performance for a low-costimplementation, thus making it desirable for mass market applications,such as the automotive industry.

It will be understood by those who practice the invention and thoseskilled in the art, that various modifications and improvements may bemade to the invention without departing from the spirit of the disclosedconcept. The scope of protection afforded is to be determined by theclaims and by the breadth of interpretation allowed by law.

What is claimed is:
 1. A rollover detection apparatus for detecting ananticipated overturn condition for a vehicle, said rollover detectionapparatus comprising: an angular rate sensor for sensing attitude rateof change of a vehicle and producing an angular rate signal indicativethereof; a controller comprising an integrator for integrating thesensed angular rate signal and producing an attitude angle, saidcontroller further comprising deployment logic for comparing theattitude angle and sensed angular rate with a variable thresholddefining a region of deployment and a region of no deployment, whereinthe deployment logic further detects the presence of a driving eventwhich causes at least one of a large attitude rate and a large attitudeangle and adjusts the variable threshold based on detecting the drivingevent so as to prevent deployment of a vehicle overturn conditionsignal; and an output for providing a vehicle overturn condition signalbased on said comparison.
 2. The rollover detection apparatus as definedin claim 1, wherein the driving event comprises a near-rollover event.3. The rollover detection apparatus as defined in claim 1, wherein thevariable threshold comprises a minimum deployment angle.
 4. The rolloverdetection apparatus as defined in claim 3, wherein the minimumdeployment angle is set to a minimum value and is adjusted to a largervalue when the driving event is detected.
 5. The rollover detectionapparatus as defined in claim 1, wherein the driving event is detectedas a function of the attitude angle and attitude rate.
 6. The rolloverdetection apparatus as defined in claim 1, wherein the deployment logiccompares the attitude angle and sensed attitude rate of change with avariable threshold curve.
 7. The rollover detection apparatus as definedin claim 6, wherein the variable threshold curve is variable based on anamount of time elapsed during a near rollover event.
 8. The rolloverdetection apparatus as defined in claim 1, wherein said integratorcomprises an infinite impulse response integrator.
 9. The rolloverdetection apparatus as defined in claim 1, wherein the angular ratesensor senses roll angular rate of the vehicle, and said controllerdetermines a rollover condition of the vehicle about a longitudinal axisof the vehicle.
 10. The rollover detection apparatus as defined in claim1 further comprising bias removal logic for removing bias from thesensed angular rate signal.
 11. A method for detecting an anticipatedoverturn condition of a vehicle, comprising the steps of: sensingattitude rate of change of a vehicle and producing an angular ratesignal indicative thereof; integrating the sensed angular rate signaland producing an attitude angle; comparing the attitude angle and sensedangular rate with a variable threshold defining a region of deploymentand a region of no deployment; detecting the presence of a driving eventwhich causes at least one of a large attitude rate and a large attitudeangle; adjusting the variable threshold based on the detection of thedriving event so as to prevent deployment of a vehicle overturncondition; and providing a vehicle overturn condition signal based onthe comparison.
 12. The method as defined in claim 11, wherein thedriving event comprises a near-rollover event.
 13. The method as definedin claim 11, wherein the step of adjusting the threshold comprisesadjusting a minimum deployment angle.
 14. The method as defined in claim13 further comprising the step of setting the minimum deployment angleto a minimum value, and adjusting the minimum deployment angle to alarger value when the driving event is detected.
 15. The method asdefined in claim 11, wherein the step of detecting the presence of thedriving event detects the driving event as a function of the attitudeangle and the attitude rate.
 16. The method as defined in claim 11,wherein the step of adjusting the variable threshold is further based onan amount of time elapsed during a near rollover event.
 17. The methodas defined in claim 11, wherein said step of integrating comprisesperforming an infinite impulse response integration.
 18. The method asdefined in claim 11, wherein the step of sensing the angular rate of thevehicle comprises sensing roll angular rate of the vehicle, andproviding a rollover condition of the vehicle about a longitudinal axisof the vehicle.
 19. The method as defined in claim 11 further comprisingthe step of removing bias from the sensed angular rate signal.